


A Merman and a Sea Unicorn Walk into a Pub...

by rane_ab



Category: Merlin (TV)
Genre: Alternate Universe - Modern Setting, Costumes, First Time, Fluff, Humor, M/M, Mermen
Language: English
Status: Completed
Published: 2013-08-30
Updated: 2013-08-30
Packaged: 2017-12-25 02:00:09
Rating: Explicit
Warnings: No Archive Warnings Apply
Chapters: 1
Words: 8,175
Publisher: archiveofourown.org
Story URL: https://archiveofourown.org/works/947284
Author URL: https://archiveofourown.org/users/rane_ab/pseuds/rane_ab
Summary: <blockquote class="userstuff">
              <p><i>Arthur was scowling, and also a merman. Merlin’s day couldn’t possibly get any better.</i> (Or, that time Merlin got to decide what their costumes would be for Morgana's annual costume party, and things didn't quite work out as expected.)</p>
            </blockquote>





	A Merman and a Sea Unicorn Walk into a Pub...

**Author's Note:**

> Originally written for the costume party bonus challenge at the [2013 Summer Pornathon](http://summerpornathon.livejournal.com).
> 
>  **Warnings** : some drunkenness, horrible amounts of silliness.
> 
> (No, really, this is a 3000-word silly fic that originally did not have any porn, and then proceeded to grow a porn scene that turned out a lot longer and cheesier than I expected. I don't understand how there are so many words.)

Arthur was scowling, and also a merman. Merlin’s day couldn’t possibly get any better.

To be fair, Arthur had been scowling ever since he’d lost the bet, making this the first year Merlin got to pick their costumes. (Why Arthur had wielded any authority over Merlin’s costume the previous years was a mystery to everyone except, presumably, Arthur. He’d always claimed it was part of their flatmate agreement. Merlin was pretty sure he was lying, but he’d have to admit to losing his copy to prove it, and he wasn’t prepared to listen to the endless lecturing about responsibility that was sure to follow.) 

This year, Merlin wasn’t wearing ridiculous feathers on his head, or a cat’s tail that everyone would feel the need to pull on, or even a garter belt (he didn’t want to talk about that one). No, this year he was going as the most noble of all creatures.

‘What _is_ that?’ Arthur said, frowning.

‘It’s a sea unicorn!’ Merlin said, grinning and puffing out his chest, because honestly, the costume was pretty awesome. He’d made it himself, mostly out of Styrofoam. It was possible he’d got carried away slightly along the way as he was working on it, and it had taken far longer than he’d counted on to make, but it was worth it: he looked absolutely majestic, if he did say so himself. 

‘A sea unicorn?’ Arthur said, staring at the large horn on top of his head. 

‘You have a _fishtail_ ,’ Merlin reminded him, glaring. Arthur did not need to know Merlin had a thing for mermen, and might have been fantasising about them since he was about nine. This was just Merlin’s revenge after years of humiliation. He deserved this.

‘Yes, speaking of, how am I supposed to walk in this, Merlin?’ Arthur said, finally looking away and shuffling along, demonstrating, his feet sticking out of a narrow hole near the bottom of the tail. 

‘You know, I think you’d make a great penguin’ was Merlin’s sympathetic opinion.

‘ _Merlin._ ’

‘Don’t worry, you’re doing great! I’m sure they’ll love you,’ Merlin said, grinning on his way out, ‘Oh, and I worked on a song for you – we can practise in the car!’ He pretended not to hear Arthur’s growl.

This was going to be fantastic.

*

It was possible Merlin had slightly miscalculated. Perhaps the shirtlessness had been one step too far. 

Unable to walk properly, Arthur had stretched himself out on Morgana’s sofa. It seemed Merlin wasn’t the only one who thought he looked like an unusually alluring fish straight out of one of his particularly wet wet dreams. There had been an endless stream of people sitting next to Arthur, stroking his tail (Merlin had made that tail, dammit! Hands off the tail!) and laughing seductively.

And here Merlin had thought he’d been slowly getting over his ridiculous (now twelve years and counting) crush. Life was just not fair, he thought, knocking back another Jaeger bomb. 

To make matters worse, his own costume had failed to make the expected (ha) splash. Gwen had given him a wide-eyed look and stammered, ‘Oh, um. That’s… an interesting choice, Merlin.’ Will had taken one look at his horn and started laughing. Then he’d looked down at where the sea unicorn’s body was curled between Merlin’s legs and there might have been actual tears.

‘This is all your fault!’ Merlin slurred when Arthur’s latest admirer got up to use the bathroom. Arthur glared at him and Merlin promptly tripped and landed in Arthur’s lap because, well, that was Merlin’s life. Something snapped. Merlin was pretty sure it was his Styrofoam tail. 

‘I swear, if one more person tries to feel me up, I’m going to beat them around the head with this,’ Arthur said, gesturing at his scaled legs. Merlin quickly removed his hands from his naked sides, then realised Arthur wasn’t referring to him and probably hadn’t even noticed. ‘And _then_ , I’m going to beat you!’

Merlin looked down at where his chest spikes were poking into Arthur’s chest hair. Arthur’s hands felt hot on his thighs where he’d grabbed on to steady Merlin after he’d fallen, and were now squeezing emphatically. ‘I don’t know what you’re complaining about. You’re the one with the irresistible costume!’ Merlin had definitely been drinking too much, because he sounded crushed to his own ears.

‘If you want to be touched in inappropriate places for the rest of the evening, I’d be more than happy to swap,’ Arthur hissed, then sighed like Merlin was the bane of his existence. Merlin felt himself drooping further. 

Arthur stared down at the broken-off piece of sea unicorn body squeezed between them, then ripped it off completely and threw it behind the back of the sofa. ‘Seriously, you look ridiculous, Merlin. Mere words cannot describe it.’ The thought seemed to cheer him up; he smirked as he looked Merlin up and down one more time. Merlin’s eyes narrowed and his nostrils flared, but before he could get a word in, Arthur started ripping the Styrofoam off the front of his costume. Merlin’s annoyance deflated, and he just stared morosely as the outfit he’d been working on for months was slowly destroyed. 

‘Now, get on here,’ Arthur said, yanking on Merlin’s legs until he was stretched out next to Arthur. ‘Since this is all _your_ fault, you can be my body guard for the rest of the evening. And don’t you dare get up. These are predators we’re talking about; I’m counting on you. I don’t care how badly you need to wee.’ He wrapped his arm around Merlin to keep him from escaping, and Merlin realised Morgana’s annual fancy dress party was well and truly over for him.

Merlin glared. Arthur grinned. It felt like the balance had been restored. 

Then Merlin frowned and said, ‘Wee? Exactly how much have you had to drink?’

‘Shut up, Merlin,’ Arthur said conversationally, and proceeded to lecture Merlin on the responsibilities of choosing a costume for one’s friend. Merlin rolled his eyes and reached up to remove his horn. ‘Oh, no, keep that on,’ Arthur said. ‘We wouldn’t want anyone to think you’re blessed with the slightest ounce of subtlety.’ He grinned and reached out to stroke his fingers along it with mock-reverence, and Merlin hated himself for not being able to suppress the shudder that ran through him at the image. So he poked his fingers into Arthur’s side where he was most ticklish to distract him, listened to him yelp right in his ear, and resigned himself to defeat in the ensuing wrestling match (though Arthur’s legs being effectively trapped turned out to be a great advantage; he made a note to look into that). 

*

The story of how Merlin had met Arthur was really quite predictable. Boy met boy. Boy hated boy. Boy tried to punch boy in the face and almost succeeded (no, really, it was a close thing, whatever Arthur said). Boy fell in love with boy. Boy did everything to hide this from other boy who appeared to be straight. It was the stuff of legend right there. Of course, other boy also proceeded to drag the first boy around with him everywhere and got him into horrible amounts of trouble that were not first boy’s fault at all (versions of this part of the story may differ). 

And they became friends, and eventually even flatmates, which had been completely fine with Merlin (well, most of the time, anyway) for many, many years. Right up until the moment he’d caught Arthur making out with Percival about five months ago. If Arthur was going to be making out with guys, it should have been with Merlin, dammit. He was Arthur’s best friend. He had _dibs_. He knew it was ridiculous, that it just came down to him not being Arthur’s type either way, but old, half-buried feelings had flared up and he had a mini-crisis, anyway, and then proceeded to force himself to get over Arthur with a renewed burst of dedication.

And then decided to dress Arthur up as a merman, as one does. Merlin did always have the best plans.

* 

He woke up half-sprawled on top of Arthur, drooling onto his naked chest. He quickly wiped it off, then tried to remember how they’d manoeuvred themselves in that position. The one where he had his nose buried in Arthur’s chest hair and was straddling his thighs. And Christ, _Christ_ , he’d just been dreaming about Arthur permanently turning into a merman and moving to the ocean, where he proceeded to try and convince Merlin to turn into a sea unicorn for real, too, by both mocking his outfit and squirming deliciously between Merlin’s thighs with his tail. 

It made sense in his dream. 

His hard-on was also still pressed pretty insistently against one of Arthur’s legs, and he hoped fervently he hadn’t been grinding down in his sleep. Probably not, since Arthur was still asleep and Merlin was still on the sofa instead of sprawled on the floor.

He groaned and started to carefully shift up when a sharp voice suddenly said, ‘Oh, finally decided to join the party again, have we?’

‘Morgana!’ Merlin yelped, and froze. He only now realised the lights were still on. Elyan shuffled into the corner of his vision, clearing up the table. Morgana was smiling in a way that didn’t make it entirely clear whether she was amused or about to gut him. 

Arthur stirred beneath him and waved a hand at the back of the couch, mumbling, ‘G’way, Morgana. Sleep.’ Merlin willed his erection to go down right this instant; it was a small miracle Arthur hadn’t noticed yet, but he would at any moment, and he couldn’t get up because _Morgana_ and also Elyan and probably Gwen, somewhere, and there was absolutely nothing erotic about this situation; he had to get a grip on himself.

Arthur chose that moment to shift in a way that pressed his thigh even more intimately to Merlin’s over-sensitive parts, and Merlin made a sound like a squirrel choking on a nut instead. 

The hand Arthur had been waving around flopped down on Merlin’s back; Arthur frowned with his eyes closed, presumably at the Styrofoam still lining Merlin’s costume there, and patted his hand downwards until he found a spot free of padding, which turned out to be Merlin’s bum, then sighed happily and settled back in.

Merlin wasn’t surprised that, even half-asleep, Arthur would make his life a misery. He’d collapsed fully back onto Arthur and his heart was beating so loudly they could probably hear it in the next town over. 

‘Hopeless!’ Morgana muttered. ‘Just so you know, you’re helping me clean the floor tomorrow. _Both of you._ ’

‘Mmm,’ said Arthur, then shifted his thigh again, like he was offering it up for a good rub. Merlin whimpered and hissed, ‘Stop that!’ before he could catch himself, then resisted the urge to slap himself. When he finally dared look up, Arthur’s eyes were still closed, the corners of his mouth quirked up slightly, like he was smirking, the bastard.

The smile melted away just before he said, ‘Just go back to sleep,’ voice rough with tiredness, and he cupped Merlin’s neck with his free hand, his fingertips brushing Merlin’s throat, and went still. Merlin lay there, thoughts in a muddle and practically panting against Arthur’s chest while the others continued cleaning up and Arthur’s breaths evened out. 

Finally, the lights went down. A minute later, Merlin shoved at Arthur’s legs until he was no longer almost humping him; he decided he didn’t care if he woke Arthur up again.

‘So, you really have a thing for mermen, then?’ Arthur somehow managed to sound both sleepy and amused, and it took Merlin another full minute to work out how he would come to that conclusion based on the limited evidence. Then he suddenly remembered: the drawing he’d made in art class once, back in secondary school, that he’d been teased about – it had been a fairly cheesy depiction of a seductive merman, and it was one of those things he’d happily banished from his memory. 

Merlin could feel his heart speeding up again, embarrassed. ‘Oh, shut up.’

Arthur snorted. ‘That’s my line. You can’t quite pull it off.’

‘I can pull it off just fine.’

‘Oh, I bet you can,’ Arthur said, and Merlin could feel his chest shaking with mirth under him.

Merlin looked up to glare at him. ‘ _Shut up._ It’s a perfectly normal… thing. Kink. Whatever. Just because you’re so unadventurous.’

‘ _I_ ’m unadventurous? Let me remind you that I’m the one wearing the merman costume you’re so lecherously getting off on. Though, granted,’ he added after a moment, ‘it really doesn’t have anything on your gigantic sea penis.’

‘It’s a _horn_ ,’ Merlin said and then realised that didn’t really sound any better and flushed.

‘Yes, you’re quite horny, I can tell,’ Arthur deadpanned.

Merlin figured it was time to get up and find a spot on the floor. Preferably in another room. But then Arthur reached up to finger his horn again, and used it to pull Merlin’s head back down to his chest while he said, ‘I’m never going to let you hear the end of this, you know. There will be mocking. For years.’ Merlin would snap something at him, except he was very aware of Arthur’s naked chest beneath his cheek, and that he was still a merman, and dammit, his hormones could go sit in a corner; he was grounding them, possibly for life. Then Arthur’s hand curved around the side of his neck again, and his fingers started stroking, very gently. Merlin’s breath caught. 

‘… Arthur? What are you doing?’

Arthur’s fingers stilled and the silence stretched, awkward. Part of Merlin was wondering whether they were ruining their friendship forever. What if Arthur was still a little drunk? He might not be so amused in the morning. ‘You know how your pervy fantasy is mermen? Well, mine is doing it on Morgana’s couch.’

Merlin snorted and relaxed infinitesimally. ‘That does sound like you.’ 

‘I just want to see the horrified look on her face, after. You know it would be priceless.’ Arthur was quiet for a while, and Merlin wasn’t sure if he was expecting some kind of answer, but then he cleared his throat and added, ‘I suppose we’d best get back to sleep before she chases us off in the morning. You know she’ll have no mercy.’

Merlin flailed a little when Arthur flipped him off; but instead of hitting the floor, he just landed with his spine against the back of the sofa. ‘You know, you’re quite heavy for a sea unicorn. The ones I’ve met before were much lighter. You should probably look into that.’

‘Maybe I’ve eaten too many mermen,’ Merlin said, poking him in the side. ‘They do taste so good.’

Arthur laughed. ‘Or maybe it’s your horn. It does seem rather unusually big.’ He threw his head back again when Merlin flushed and narrowed his eyes.

‘Oh, go to sleep.’ Merlin shifted around, trying to get comfy.

‘I was asleep,’ Arthur said, wrapping an arm around Merlin to keep him still, ‘and you woke me up. _Twice._ ’ His hand somehow landed on Merlin’s arse again. ‘So you shut up and go to sleep. And keep your sea penis under control.’

Merlin shoved him, then skimmed his fingers down Arthur’s side again in obvious threat. ‘I know your weaknesses, Pendragon. Don’t tempt me.’ 

‘And I know yours,’ Arthur said, sounding smug. Merlin wasn’t expecting the press of lips against his. It was clumsy and not really that comfortable, and over before he well and truly realised it, but it left his heart trying out for another marathon, nonetheless. ‘So good night!’ Arthur added after a few seconds, and he actually sounded a little bit awkward. 

‘Good night,’ Merlin replied after the moment had stretched for too long. Arthur grumbled something about wretched sea unicorns who wouldn’t let him sleep, and what he’d give to be at the bottom of the ocean, but then his nose brushed Merlin’s when he tried to pull him a little closer to settle in, and Merlin laughed. 

‘One word,’ Arthur said, ‘and you’ll never get to kiss a sexy merman again.’

So Merlin smiled and went to sleep. 

*

Of course, the next day, Arthur put more work into bossing Merlin around than actually cleaning the floor, all on account of his tail (according to him). 

He didn’t mention the kiss, if it could be called that, though he did keep his promise about the teasing (apparently, Pendragons always kept their promises, even if it involved accompanying their sisters to a bachelorette party that looked like it might get badly out of hand, wearing far too few clothing items and far too much oil as the price of entrance. Merlin still had the pictures he’d begged off Morgana on the pretence that they would make great blackmail material. Actually, they did turn out to make great blackmail material – amongst other things). 

Merlin was relieved things were not awkward between them, he decided, and incinerated the hope he’d allowed to flare up inside him along with his costume, right there in their back yard. 

He only singed his eyebrows a little bit, and decided to count it as a win.

*

They didn’t talk about it for the next two weeks, things settling back into their usual routine, which was probably why when Merlin came home from work that Friday, the last thing he expected was to find Arthur in his bed wearing nothing but the tail and flapping it seductively at him. And why he walked straight into the half-open door in shock.

‘Seriously?’ said Arthur, sighing. 

‘What are you doing?’ Merlin eyed him in bewilderment while holding his poor head. 

He followed the light pink flush as it spread down Arthur’s chest and up over his cheekbones with surprised interest (honestly, he might have considered it being the result of Arthur having some kind of allergic reaction to Merlin’s fabric softener, except for the part where they used the same fabric softener since Arthur liked to sneak his clothes in with Merlin’s, then complain about the appalling service when Merlin just dumped his clean but wrinkled clothes on his bed. They’d developed a certain routine after all these years), but before he could comment on it, Arthur spread himself back out on the bed like he thought Merlin was a painter, and he was the particularly shameless and showy model who’d got fishnets and fishtails confused. Merlin could sympathise with the feeling.

‘Well, it’s your birthday, and you did mention you wanted fish for dinner.’ He gestured down at himself as if to say, _voilà_.

‘Um.’ Merlin stared at Arthur, half-naked in his bed; he looked more than a little bit ridiculous, truth be told, cocky smirk and all, but Merlin’s heart went _thump thump thump_ like it meant business, anyway. ‘And you were too lazy to cook?’

‘Oh, for – _yes_ , Merlin, I was too lazy to cook, so I thought perhaps you could cannibalise me. I left the condiments in the kitchen; you’ll have to forgive me.’ Arthur looked offended now, arms crossed in front of him, flush deepening. He wiggled for a moment like he was going to get up, but then froze again, probably because he realised how silly it looked.

It made Merlin feel like he was on more equal footing, and he stepped closer to the bed, sucking his lower lip into his mouth nervously. He couldn’t quite help looking from the corner of his eye: Arthur’s arse looked amazing in the tail. ‘I don’t think it’s considered cannibalism if you’re not human.’

Arthur wasn’t looking at him anymore, instead glaring down at the bedding, and Merlin sank down on his knees next to the bed. His bed, which Arthur was in, his skin pressed into Merlin’s sheets that would probably smell of him later. The weird flutter in Merlin’s belly cautiously made itself comfortable, against his better judgement, sprawling out through his limbs and making his fingertips prickle. 

‘Arthur,’ he said, and the words had a little trouble making it out of his mouth. ‘What are you doing?’

Arthur glanced up at him, looking mulish now. ‘It was supposed to be a surprise for your birthday. Ta-fucking-da.’

‘That I was going to have to sleep on the floor tonight because my bed is occupied?’

‘No, you idiot,’ and yep, that sounded more like Arthur right there, ‘You’re into mermen, aren’t you? So now there is one in your bed. I’m providing you with the perfect, impossible gift. I am an amazing friend, I’ll have you know.’ He said the last bit with conviction and not a little bit of hurt pride, and oh, there was the pout. It was a thing he did and one which Merlin would have mocked him for till the end of their days if it didn’t also make him a little too happy in the trouser area. It was probably a sign of just how hopeless he was, but he preferred not to linger on that.

‘You are an amazing friend,’ Merlin said, because if nothing else was true, that part was, even leaving his birthday gift aside. Arthur might be an ass sometimes, but he’d always been there for Merlin when it really counted (like that time he’d been dumped after a whole four-month relationship, and Arthur cheered him up by buying at least three bottles of alcohol, then jumping naked into the Thames with him, as proof that they were still alive and also daring young men. It had been unexpectedly nippy, it being the middle of March and all, but by the time they’d finally managed to make it back out again, Merlin had forgotten there were reasons for him to cry other than his bollocks freezing off. The solemn, manly slap to the back Arthur had given him while refusing to acknowledge their teeth were chattering so hard they might break had confirmed it was time for him to move on if he wanted to get out of this with body and sanity intact). 

When Arthur started looking smug, leaning back and subtly stretching out on the bed again, Merlin realised he might not have been very subtle with his ogling just then. 

‘I am,’ Arthur said magnanimously, and after a moment stretched out his arm to warmly cup the back of Merlin’s neck. It brought back too many memories of the costume party and Merlin felt the heat in his cheeks spreading through the rest of his body. When Arthur just kept looking at him, Merlin said, feeling himself shake a little, ‘I thought you were straight.’

Arthur shrugged, not quite meeting his eyes. ‘I’ll make an exception for your birthday.’ It was both a blatant lie of omission, and a hint that maybe, maybe he did plan to do more than just lie there in Merlin’s bed. Maybe Merlin’s hope wasn’t completely blinding him and making him misread all the signals. 

Fuck it, he thought, and leaned forward. 

Their noses clashed, and Arthur pulled back, breathing out sharply; his hand was still on Merlin’s neck, though, so Merlin dived back in, getting up to lean over the bed, trying to adjust, Arthur’s mouth so close and the want heavy in Merlin’s stomach. It would not be Merlin’s life if he didn’t overbalance and land uncomfortably on top of Arthur, nowhere near his mouth. 

‘Sorry, sorry,’ he mumbled, trying to get up so he wouldn’t be crushing anyone anymore, and put a hand down to push himself up; unfortunately, it turned out he was using Arthur’s crotch as a crutch. 

Somehow, Arthur did not see the joke. The sound that came out of his mouth might have been ‘Meaaarkill,’ but it was kind of hard to tell.

Merlin was contemplating just letting himself slip off and under the bed and file for cohabitation with the dust bunnies and stray socks when Arthur took over and started yanking at him until he wasn’t pressing down anywhere uncomfortable anymore. Of course, now he was also straddling Arthur, which was in no way awkward, because he’d decided he just wasn’t going to look away from Arthur’s belly button, which looked a little funny, really, when you squinted and looked at it sideways, so there. 

He broke his promise almost immediately when Arthur’s chest started shaking, just in time to see Arthur throw his head back and laugh out loud. ‘Oh my God, you are so hopeless. Do you constantly trip over everyone, Merlin, or am I special? Don’t answer that, of course I’m special.’

Merlin shoved him. ‘It was an accident! No need to be cruel. It’s my birthday, remember?’ And then, because he’d never known when to shut up (or at least, let the knowledge stop him), ‘Besides, you’re the merman, aren’t you supposed to be seducing me?’

‘Mermen are heartless creatures,’ Arthur said, grave, clapping a hand over his chest. ‘I’m sorry, I can’t help it, it’s in my nature.’

‘It’s in your nature to be a bully, that I can believe.’ Arthur let out an offended shout and grabbed Merlin’s head, trying to rub his knuckles over the top it. ‘Yes, thank you for proving my point,’ Merlin tried to say while wrestling off Arthur’s grip, but it got a lost in his chocked laughter. 

‘As for the seduction part,’ Arthur said moments later, and stared deeply into Merlin’s eyes. Merlin swallowed, the fluttery feeling coming back in spite of himself. Then Arthur started to sing. ‘Oh ye weary traveller, watch me wag my tail, my eyes say come hither, I shall make you wither, and off to the bottom you sail – ’ It was the ‘song’ Merlin had invented especially for him, and let it be known to the world that Arthur? Arthur could not sing. Though it didn’t stop him from cheerfully continuing to massacre the beautiful lyrics that had come straight from Merlin’s soul, deep in his bones – though mostly his funny bone. 

Merlin was almost crying with laughter when Arthur waggled his eyebrows. ‘Well, is it working yet?’ Except then he actually made a grab for Merlin’s crotch, presumably to check, making Merlin shout in turn, and Arthur laugh some more. ‘Ah, revenge really is as sweet as they say.’

‘Oi!’ Merlin poked him in the side vindictively. ‘I still know your weaknesses, merman!’

Arthur grabbed his wrist and eyed him. ‘You don’t stand a chance, and you know it, you scoundrel!’ Merlin made a move for Arthur’s other side, only to get intercepted there, too, and Arthur started making mocking kissy faces at him. Only Merlin got distracted by staring, and the mirth slowly evaporated, replaced with the earlier tension. Arthur’s hand curled around Merlin’s neck again, he allowed himself to be tipped forward, his heart making another sudden sprint for his throat. He could feel Arthur’s breath on his face, and Arthur’s other hand came up to cup the side of his face, which helped not at all with how hot Merlin was feeling. 

‘Hey,’ Arthur said, because regardless of his claims concerning Merlin, he was really the most ridiculous.

‘Hi.’ Merlin wondered if it was possible for his heart to actually crawl into his mouth. It seemed to be making a valiant attempt, but before he could follow that thought down the rabbit hole of madness, Arthur’s hand left his neck to frame his face, until he had a solid grip, and tilted Merlin’s head just so, before pulling him all the way down. 

There were no more accidents on the way to Arthur’s mouth, and there it was, shocking, sweet, perfect. Well, it was no more than a light brush of lips, but it was _Arthur_ and twelve long years of imagining exactly this (and he hoped fervently Arthur would never find out how many times Merlin had wanked to this, because he would either disown Merlin or his head would never fit through the door again; it was a toss-up which), and he could feel gooseflesh forming over his back and up on his scalp, which felt strange in the best kind of way. 

The next press was firmer, and this was really happening; Merlin’s brain might as well be somewhere on the other side of the room flailing in a corner for how much coherency he retained in that moment. Arthur’s lush lips were just as soft as he’d imagined, and the gooseflesh ran down the backs of Merlin’s thighs, happy and eager, the bottoms of his feet starting to prickle. 

Arthur was still holding him, and Merlin let him guide the kiss, softly pressing their mouths together over and over again, content to take what he could get, and not wanting to overstep Arthur’s comfort zone. But then Arthur pushed him back to breathe for a bit, and oh, the gentle flush over his cheeks and the bridge of his nose made Merlin’s mouth go dry. He was staring up at Merlin with half-lidded eyes, and the tip of his tongue came out to wet his lips, and – fuck. When Merlin tried to lean back down, Arthur let him. Merlin kissed him thoroughly, reverently, and then when he thought of Percival, as dirty as he could make it, because damn if Merlin wasn’t going to be the best kiss Arthur would ever get from another guy. Or, if he could make it so, from anyone. 

He didn’t know what this was – _I’ll make an exception for your birthday_ , Arthur had said – but if this was it, he wanted Arthur to remember it. It seemed like he might, considering he was returning the kiss with equal fervour; Merlin shivered when he felt Arthur’s warm hands stroking gently down his back, occasionally gripping tight, until he pulled back to pant into the small space between their mouths. Merlin couldn’t resist going back for another brief taste after just a moment. 

When he opened his eyes, he noticed the corners of Arthur’s mouth were quirked up, and he looked far too amused for Merlin’s liking. ‘What?’

Arthur raised his eyebrows. ‘Who knew you’d be that competitive in bed? Or is it that the costume _really_ gets you going?’ He flapped his tail a little, jarring Merlin. Arthur’s smile spread when Merlin scowled at him. ‘It really does, doesn’t it? Have some self-control, Emrys,’ he said, mock-sternly, ‘We have all night, you know.’

‘We do?’ Merlin felt slightly mollified, and tried to squash the hope blooming in his chest.

‘Didn’t I tell you this was the perfect birthday gift? Now tell me how handsome I look.’ 

Merlin snorted. ‘You make a very pretty merman.’ Arthur pulled a face, but Merlin sat up, making sure to cop another thorough look, because he might as well enjoy the moment. This was probably the one and only time he’d get a proper go at a merman. And Arthur did look exceptionally good like this. He imagined them sprawled out on a (surprisingly soft) rock in the middle of the ocean, Arthur having just lured him in and Merlin being unable to resist his call, out of his mind with want. It was a little too easy to get into the fantasy, and Merlin’s throat clicked.

‘Which reminds me,’ Arthur said, making a grab for the nightstand, ‘before we continue…’

It wasn’t quite what Merlin was expecting. His eyes widened. ‘I thought I’d burned that thing.’

‘Don’t be ridiculous, it’s plastic,’ Arthur said, and did the honours of sliding the horn back onto Merlin’s head. ‘There you go. Makes the experience so much more authentic, don’t you think?’

‘I hate you,’ Merlin said, and wished he meant a word of it, and that the fact that Arthur had saved the stupid thing and that his mind had no problem whatsoever adapting the fantasy to the tragic (but extremely hot) tale of a merman and a sea unicorn who were meant to be in spite of their differences didn’t turn him on even more.

‘Oh, but Merlin,’ Arthur laughed, ‘you have the prettiest sea penis of them all.’ 

Merlin narrowed his eyes, because he never could resist a challenge when it came to Arthur. He hissed, as threatening as he could make it, ‘And I’m going to stab you with it.’ 

‘Is that a promise?’ Arthur said, almost too quickly; and there it was again, the faint, magical blush that his grin couldn’t quite cover, and the way his eyes slid away for a moment. He seemed to realise his mistake because when Merlin opened his mouth, Arthur pulled him back down; Merlin’s horn collided with Arthur’s head, and he growled ‘ _Merlin_ ’, making a show of his exasperation even though none of this was Merlin’s fault. 

Still, Merlin decided to let it go because he was a generous soul.

Arthur seemed determined to prevent Merlin from breaking away and continuing that conversation, which was presumably why he was groping Merlin’s arse in no time, not that Merlin was complaining or anything. By the time Arthur started to calm down, things had also seriously heated up; Merlin’s mouth felt pleasantly bruised, the back of his neck hot where Arthur had kept him close, and his back and his bum tingled pleasantly where Arthur had been stroking up and down. 

Merlin hovered over him, unsure whether Arthur was ready for a next move, and spread his fingers over Arthur’s chest, hesitating. It only took so long before Arthur’s bossy side could not be suppressed: he grabbed one of Merlin’s hands and rubbed it curiously before stroking it just below his throat, looking at Merlin, apparently doing the exploring for him. He pressed Merlin’s fingers over one of his nipples; Merlin squeezed and Arthur’s breath hitched, though being Arthur, he pretended nothing had happened, and moved Merlin’s hand further, low on his stomach, just above the waistband of his tail. Merlin could feel the muscles twitching beneath his touch. 

He wanted to make a wise crack to break the odd silence, but found that he couldn’t, not with Arthur looking up at him like that, eyes soft and wide like he was maybe a little surprised, his mouth open, breaths coming in and out quickly. And Merlin was greedy, wanted so much more. He gave up the sight of Arthur’s face for the taste of nipple, felt the quick rise of Arthur’s chest.

Arthur jerked up against him and let out an unexpected moan that sounded loud in Merlin’s ears; his blood felt too hot for his body, and it all seemed to be going so fast all of a sudden, like they’d been pulled under the waves of the ocean, now, and there was no way back out again. Arthur’s fingers were buried in his hair, keeping him in place, and he felt dizzy when he realised he could feel Arthur’s arousal poking him in the stomach.

Arthur yanked at his shirt, and it took Merlin a while to find the coordination to take it off. Arthur was laughing again by the time he managed it, albeit somewhat breathlessly, probably because he could feel his hair sticking up every which way and because Arthur had to slide the horn back on; Merlin’s heart squeezed, because Arthur looked impossibly beautiful, flushed and aroused and spread over Merlin’s bed, dressed up as a merman just because he could; all jokes aside, it was possibly the sweetest thing anyone had ever done for him. Arthur deliberately stroked down Merlin’s belly, following his happy trail, and dipped just the tips of his fingers under the waistband, teasing, and Merlin just wanted to make him happy, and if that involved this moment never stopping, he’d sign up for that, soul and all. 

Still, a shove was all it took for him to stumble off Arthur so he could take everything off without kneeing anyone in mood-killing places. The sudden distance made him oddly nervous; his skin felt electric, and it wanted to be closer to Arthur, now. He should probably look into that tail and make sure it didn’t actually come with magic merman wiles. 

When he finally pulled off the last sock, Arthur was blatantly staring at him, his gaze lingering where Merlin’s cock was happily bobbing against his stomach as he climbed back onto the bed. Merlin felt a little embarrassed; wondered how many stiff cocks Arthur had seen in his life, aside from his own. He knew he had nothing to complain about, but right now it just made him nervous that it might put Arthur off, somehow; wished, perhaps for the first time in his life, that he was smaller, more unobtrusive.

He straddled Arthur again lightly, wanting to give him the chance to tell Merlin no if he wanted to, but he seemed fascinated by the way Merlin’s prick moved around, following it with his eyes. ‘Seriously,’ Merlin said, blushing, ‘you know you have one too, right?’ 

Arthur did not ask for permission to touch, but then again, Merlin’s cock practically leaped into his grip when Arthur’s fingers grazed him. He jerked Merlin off a few times, hesitant, and then more confidently, and Merlin kept waiting for the other shoe to drop, for the clever insult, something, anything. When it didn’t come, he couldn’t help saying, ‘If you want me to come in about a minute flat, you’re going about it perfectly,’ closing his eyes to try and maintain some control.

‘No stamina, Merlin? We’ll have to come up with a plan to train you,’ came Arthur’s voice at last, and it sounded rough, Arthur’s gaze shifting to his briefly before going back to his cock, and Christ, but he looked entirely too fascinated for Merlin’s sanity and self-control.

‘Oh?’ was about as much as Merlin managed, as Arthur’s grip turned teasing, playing with the foreskin and rubbing it over the head, and Merlin only now realised he’d spread his own legs wide to give Arthur the best access, that for all his embarrassment he was exposing himself fully, pushing into the touch with dedication; that the muscles in his thighs had started to strain with the effort and it was doing nothing to stave off his orgasm, or to prevent the strangled whimper that fell out of his half-open mouth.

‘Don’t worry, I have some ideas,’ Arthur said. ‘We’ll have to make a schedule.’ He finally pulled away to trace his fingers down the inside of Merlin’s thigh, and Merlin could no longer tell if Arthur’s cheeks were actually that red or if his wavering sight was betraying him into seeing the flush run straight down the middle of his chest and under the waistband of the costume. 

‘A schedule? Will I never be rid of you, then?’ He meant it to come out teasing, but instead it was just breathless. 

Arthur looked up at him and he could only imagine the picture he made: naked, shamelessly exposing himself, his cock red and wet; he could feel his eyes open too wide and too greedy, the way his skin burned and his blood somehow seemed to be flowing through his veins thickly, throbbing with his heartbeat, and it felt like it had to be visible just under his skin. 

‘If you work really hard,’ Arthur said, tracing his knee, and looking away for a second, ‘and for a really long time. You might just get lucky.’ 

‘Yeah?’

‘You’ll have to put in a lot of hours first, though. And we all know how flaky you are, Merlin. Not to mention a slow learner.’ Arthur’s chin jutted out in that way that was a dead give-away for when he pretended to be braver than he felt, and Merlin’s heart tripped over itself for reasons that had nothing to do with their state of undress.

‘Yeah, might take a while,’ Merlin said, and his throat ached, no matter how many times he swallowed, ‘Maybe the rest of my life?’

‘Wouldn’t surprise me a bit,’ Arthur said, giving Merlin a look that was only slightly mocking, and Merlin could feel his own pulse jump in his throat; grabbed Arthur’s hand and pressed it there thoughtlessly. 

It calmed him down enough that he could say, after a while, solemn, ‘So you really like my sea penis, then?’

For a second, Arthur’s face twisted in denial, then closed down, and then helplessly rearranged itself into a grin. ‘Yes, Merlin, it’s really the prettiest of them all. You didn’t exaggerate.’ He looked up at the horn on Merlin’s head. ‘Much.’

‘You’re an ass, and I still hate you,’ Merlin said, with no heat whatsoever, rubbing first his neck and then his cheek against Arthur’s hand, pretending like that was a sane thing to do (Arthur had lovely hands, and it was absolutely a sane thing to do). 

‘Wouldn’t have it any other way. Don’t think I’ll always be indulging you like this, by the way,’ he said, squeezing one of Merlin’s thighs, ‘Wouldn’t want you to get complacent. Besides, this outfit is going to be thoroughly ruined after one go. So you’d better enjoy this.’ 

Merlin paused. ‘Hm. I suppose you have a point about that last bit,’ he said, then climbed off Arthur again and tried to pull Arthur on top of him. ‘Come on!’ 

Arthur huffed, impatient. ‘Enjoying ordering me around, are we? Bossy.’ Merlin was expecting more protest at the fuss, really, but in the end Arthur just said, ‘Like this?’, his hair sticking from where Merlin had run his hands through it, giving Merlin a smile that came out ridiculously fond and only a little bit exasperated, and Merlin could feel his own grin stretch wide.

‘Yes, if that’s all right, Mr Merman, please.’ He fluttered his eyelashes for effect.

Arthur snorted. ‘Sure,’ he said, getting comfortable between Merlin’s thighs and yep, a little too much like his fantasies; he expected he was going to be paying this back in spades in the coming weeks, and the thought made his stomach swoop pleasantly.

At least Arthur was back to looking superior, amused at Merlin’s antics, grinning obnoxiously. ‘Hm, what do you want me to say?’ Merlin pulled him down and they kissed for a while, Merlin moaning and arching up, getting used to the pleasant weight of Arthur on top of him. Then Arthur leaned close to his ear, seemed to hesitate for a moment, and in a rough whisper said, ‘Hello, little boy. You are mine now. I’m taking you to the bottom of the ocean to play, and I’m _never_ letting you go,’ which was probably when Merlin lost his last coherent thought. 

Or it might have been when Arthur then bit the side of his neck possessively, and words fell out of Merlin’s mouth that might have been, ‘Christ, yes, please,’ but honestly, who was keeping track, because it wasn’t Merlin, that was for sure. 

He tipped his head back eagerly, giving Arthur room to bite and suck at his leisure. Arthur said something that might have been, ‘Knew you really liked it, gah,’ but he didn’t pause long enough to enunciate clearly, and Merlin didn’t care. He could feel the alternately slick and slightly rough material of the tail between their cocks, catching in unexpected ways, slightly uncomfortable yet somehow just right. He thought of them, down at the bottom of the ocean, of the fantasies that had fuelled to many orgasms. But mostly there was the reality of Arthur, the fantasy he’d never allowed himself to believe too hard, who was right there rocking between his thighs, who was warm and solid beneath his hands.

‘I know you know this, and don’t let this go to your head or I’ll have to do something drastic, but fuck, you’re so hot,’ Merlin breathed, unable to help himself, and Arthur just whispered, ‘Yeah?’ looking far too pleased but not nearly as smug as he should have been, rocking his hips more slowly, more deeply, and he looked every bit as undone as Merlin felt. 

He remembered he was still wearing the horn when Arthur pressed his hand down on it, keeping his head pinned, sucking at his Adam’s apple and humping him urgently, and the tingling feeling running from his throat to his balls to his feet suddenly decided to invade his teeth, too, and his palate, and then it was everywhere and Merlin was drowning in the unbearable feeling of it, groaning and pulling Arthur close, closer, holding him tight, and then he was coming, spurting between their bodies making the slide of them slicker. 

‘Good?’ Arthur said, then leaned down to give press a stupidly chaste if lingering kiss onto Merlin’s slack mouth while holding on to the horn, a tense line over Merlin’s body. ‘ _Fuck_ yeah,’ Merlin said, feeling a happy laugh bubble up out of him, and he collected enough brain cells to grab Arthur’s neck in turn, rub his thumb over it and squeeze his arse with his other hand, urging him on, and then Arthur went taut. Possibly the most ridiculous sound Merlin had ever heard came out of his mouth, and he felt weirdly gratified that Arthur wasn’t entirely perfect, was perhaps not completely out of his reach; most of all, he felt immediately fond of the sound, protective of it, wanted to hear it again and again and make it his.

After, Arthur lay on top of him, panting, and then there was a kiss to the side of his throat before Arthur slipped off, pulling a face, and then pushing off the tail, thoroughly ruined, as predicted. 

‘Next time, we’re doing my thing.’ Arthur grinned, still panting a little, and pressed another kiss to Merlin’s arm. ‘You didn’t look half-bad in that cat tail.’

‘ _Seriously_? You’re going to make me pay for this, aren’t you?’

‘Mmm, I think it’s been proven quite convincingly that you should never be in charge of costumes, Merlin. Leave it up to me from now on. Besides, we have your training to attend to.’ 

‘I don’t think I did that badly,’ Merlin huffed. He looked over when Arthur didn’t say anything. ‘Hey.’ Merlin elbowed him.

‘That’s all right, then,’ Arthur said a little too cheerfully. ‘We don’t have to do this again if you don’t want to.’

‘Arthur,’ Merlin said, disbelieving. ‘I’ll wear the bloody cat suit if that’s your thing. Fuck, I’ll wear the garter belt. Though you never get to lord any of those pictures over me ever again,’ he added as an afterthought, poking Arthur in the chest for emphasis. ‘You’re the one who’s been insisting he was straight up until recently and _then_ went around kissing overly muscly friends and never mentioned any of that to me. So, you know.’

Arthur blinked at him. ‘I’ll let Percy know you’re not his type, then.’ Merlin might have growled a little. ‘The cat tail’s a really good look on you,’ Arthur said, smiling a little. ‘We could try that sometime. And for the record, I have never insisted I was straight. I was just – making sure. With Percival. Who is really hot, too, by the way.’

‘Are you sure you wouldn’t rather hook up with him?’ Merlin pouted.

‘Well, I did think about it, but we’re already living together, so you’re just a lot more convenient.’ He waved a bored hand for emphasis, and Merlin threw a pillow at his head.

‘Bastard,’ he said, while Arthur started laughing, so Merlin hit him with the pillow again.

This was why he was running through their flat naked, Arthur hot on his heels, armed with the pillow, when he saw the kitchen table, and the candle in the middle of it. It was in the shape of a sea horse, and someone had glued a large horn to its head. 

‘… You are really never going to let this go, are you?’

‘Not even if we turn a hundred.’

Merlin looked at him sideways. ‘You think we’ll still know each other if we get that old?’

‘Excuse me, did I not just lure you under my spell and bind you to me forever?’ He pointed a thumb back at the bedroom. ‘Pay attention, Merlin.’

‘You wish!’ Merlin said, glaring, and then started running after Arthur while brandishing the candle in front of him. ‘Don’t anger the sea unicorn! Or it will pierce you with its horn…’

‘Which certainly sounds like really bad porn,’ Arthur singsonged along before throwing himself on the bed. ‘I’m still waiting for that, by the way. I seem to recall a certain promise on your part…’

‘Didn’t you say we had all night?’ Merlin grinned and put the candle down on his nightstand. 

It stayed there the next day, and the next year, and all the years after that. Arthur swore it would be the candle on his one-hundred-year birthday cake. And Pendragons did always keep their promises.


End file.
